The first answer here should cover it:
https://askubuntu.com/questions/910037/where-is-the-vlc-logfile-for-errors
Tools → Preferences → way down at the bottom: select the “all” checkbox
top left then is: Advanced - and below that: Logger
check: log to file - give it a name and location or choose an already existing file …
Starting vlc from a terminal rather than via the menu could also give some helpful output in that terminal - I don’t know.